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Date:      Thu, 12 Sep 2002 22:04:44 -0400
From:      "Mark W. Krentel" <krentel@dreamscape.com>
To:        freebsd-stable@freebsd.org
Cc:        dillon@backplane.com
Subject:   Linux dump in 2.4 kernels
Message-ID:  <200209130204.g8D24ib70307@dreamscape.com>

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A thousand pardons for bringing up a Linux issue here.
I just wanted to correct something I said earlier.

A couple months ago, there was a thread on -stable about ext2 dump in
the Linux 2.4.x kernels.  See "Glacial speed of dump backups" around
July 23-25.  I claimed that the cache design in the 2.4.x kernels made
it impossible for ext2 dump to work correctly on an idle but mounted
file system.  This is not correct.  There were bugs in the early 2.4
kernels that caused the problems I was seeing.  But they were bugs,
not a design decision that would deprecate dump, and many of them have
since been fixed.  I misinterpreted some of my conversation with the
Linux dump maintainer which led to my erroneous conclusion.

I'm not saying that all such bugs have been fixed.  I've seen problems
as late as RH 7.3 (2.4.18 kernel).  I'm just saying that ext2 dump is
supposed to be viable on a mounted file system, provided of course,
the file system is idle, you sync(), etc.  And if it's not, then it's
a kernel bug.

My advice to people running dump in Linux is to upgrade to both the
latest kernel and the most recent dump release.

I'd also like to apologize to Matthew Dillon for not believing him.
Matthew said (regarding dump), "I do not know of any issues with Linux
that make it any different from FreeBSD.  If you sync a couple of
times dumping an idle filesystem under Linux ought to work just about
the same as dumping an idle filesystem under FreeBSD."  At the time,
I didn't believe him, so I apologize.

And please, I don't want to start a big thread on this.
dump-users@lists.sourceforge.net would be a great place for further
discussion.  I just wanted to correct one piece of FUD I may have
said.

--Mark

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